Spin configuration in isolated FeCoCu nanowires modulated in diameter

Cylindrical Fe28Co67Cu5 nanowires modulated in diameter between 22 and 35 nm are synthesized by electroplating into the nanopores of alumina membranes. High-sensitivity MFM imaging (with a detection noise of 1 µN m-1) reveals the presence of single-domain structures in remanence with strong contrast at the ends of the nanowires, as well as at the transition regions where the diameter is modulated. Micromagnetic simulations suggest that curling of the magnetization takes place at these transition sites, extending over 10–20 nm and giving rise to stray fields measurable with our MFM. An additional weaker contrast is imaged, which is interpreted to arise from inhomogeneities in the nanowire diameter

Electrochemical synthesis and magnetic characterization of periodically modulated Co nanowires

The synthesis of templates with modulated pore channels by combined mild and hard anodization processes is described. The hard anodization pulses, implemented during anodization, are controlled not only in time length and amplitude, but also in shape: square and exponential signals have been applied. Electrodeposition of Co is subsequently performed to obtain uniform and modulated diameter nanowire arrays. Square and exponential modulated diameter nanowires are imaged by scanning electron microscopy and hcp hexagonal polycrystalline structure is confirmed in all Co nanowires. Magnetic behavior strongly depends on nanowire shape and is interpreted considering the modification of magnetostatic interactions between wires induced by local stray fields from magnetic charges at the ends of the wider segments in modulated wires. As a consequence, magnetization processes under parallel and perpendicular field configurations denote the contribution of both thin and wide segments. © 2014 IOP Publishing Ltd.The support of the Ministerio de Economia y Competitividad of Spain under projects MAT201002798C0501 and C0503 is acknowledged. Ignacio Mínguez Bacho thanks the Spanish National Research Council (CSIC) for a JAE-preDoc fellowship cofinanced by the European Social Fund.Peer Reviewe

Thermal instability of implanted Mn ions in ZnO

5 pages, 4 figures.This letter reports on the site configuration of implanted Mn cations in ZnO. The samples studied were obtained by means of ion implantation in m-plane ZnO single crystals. Synchrotron radiation based fluorescence shows no contamination during the implantation process. The results of micro-x-ray absorption spectroscopy indicate that Mn ions are located in substitutional sites without detectable traces of secondary phases. The postgrowth thermal annealing in O2 atmosphere induces a change in the coordination of a large amount of Mn cations, corresponding to alpha Mn2O3The authors thank to Professor M. Vazquez for financial support.Peer reviewe

Influence of sulfur incorporation into nanoporous anodic alumina on the volume expansion and self-ordering degree

Self-ordering degree of anodic alumina nanopores is related to the volume expansion of the aluminum oxide. However, little is known about how the ionic species derived from electrolyte affect parameters inducing self-ordering of the nanopores. The influence of sulfur incorporation into nanoporous anodic aluminum oxide (AAO) films on volume expansion and self-ordering degree has been investigated under potentiostatic conditions (14-25 V) in different sulfuric acid electrolytes (3-20 wt %), the average current densities of each anodization being in the range of 0.1-10 mA cm. Rutherford backscattering spectroscopy (RBS) reveals that the incorporation of sulfur species into AAO, as well as the volume expansion factor (VEF), follows a logarithmic dependence on the average current density regardless of the applied voltage and sulfuric acid concentration. The relationship between volume expansion and the S/Al ratio is linear for each concentration of acid in the electrolyte. Furthermore, self-ordering regimes are also revealed for each acid concentration at VEF in the range of 1.50-1.66. We suggest that plasticity, enhanced by sulfur incorporation, counterbalances the high mechanical stress generated by volume expansion, thus inducing new self-ordering regimes. These new regimes are dependent not only on VEF but also on a subtle equilibrium between stress and plasticity of the nanoporous AAO films.Work supported by the Spanish Ministry of Science and Innovation under project MAT2010-20798-05-01 and 05-05. The authors wish to thank the support from the Ministry of Education in Singapore under the AcRF Tier 2 (MOE2014-T2-1-132). I.M.B. thanks the Spanish National Research Council (CSIC) for a JAE-preDoc fellowship cofinanced by the European Social Fund. M.H.-V. thanks financial support under project CCG08-UAM/MAT-4024

Spin configuration in isolated FeCoCu nanowires modulated in diameter

Cylindrical Fe28Co67Cu5 nanowires modulated in diameter between 22 and 35 nm are synthesized by electroplating into the nanopores of alumina membranes. High-sensitivity MFM imaging (with a detection noise of 1 µN m-1) reveals the presence of single-domain structures in remanence with strong contrast at the ends of the nanowires, as well as at the transition regions where the diameter is modulated. Micromagnetic simulations suggest that curling of the magnetization takes place at these transition sites, extending over 10–20 nm and giving rise to stray fields measurable with our MFM. An additional weaker contrast is imaged, which is interpreted to arise from inhomogeneities in the nanowire diameter

Variation of the refractive index by means of sulfate anion incorporation into nanoporous anodic aluminum oxide films

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Variation of the refractive index by means of sulfate anion incorporation into nanoporous anodic aluminum oxide films

The variation in the refractive index of nanoporous anodic aluminum oxide (AAO) films regarding the sulfur anion incorporation is studied in this work. For this purpose, different samples are grown under potentiostatic conditions at different voltages and concentrations of sulfuric acid in the electrolyte. The samples are analyzed by Rutherford backscattering spectroscopy and infrared spectrometry, confirming the presence of sulfate anions and water embedded into the nanoporous AAO films. The incorporation of sulfate ions into the alumina matrix varies from 6.3 up to 11.7% regarding aluminum content. We have studied Fabry-Pérot optical interferences by shining incident monochromatic light in specular reflectance conditions. The reflected monochromatic light waves interact in internal reflectivity generating constructive and destructive interferences known as Fabry-Pérot optical interferences. An iterative method based on the equation for constructive interferences conditions in thin films and Snell equations is developed in order to calculate the refractive index of the nanoporous AAO films as a function of the wavelength. The calculated refractive indices increase when the sulfur content of the nanoporous AAO films decreases. The variation of the calculated refractive index is 0.08 and remains constant in the wavelength range 400-1200 nm.Work supported by the Spanish Ministry of Science and Innovation under project MAT2010-20798-05-01 and 05-05. The authors wish to thank the support from the Ministry of Education - Singapore under the AcRF Tier 2 (MOE2014-T2-1-132). Ignacio Mínguez Bacho thanks the Spanish National Research Council (CSIC) for a JAE-preDoc fellowship co-financed by the European Social Fund. Manuel Hernández-Vélez thanks financial support under project CCG08-UAM/MAT-4024

Spin configuration in isolated FeCoCu nanowires modulated in diameter

Cylindrical Fe28Co67Cu5 nanowires modulated in diameter between 22 and 35 nm are synthesized by electroplating into the nanopores of alumina membranes. High-sensitivity MFM imaging (with a detection noise of 1 μN m−1) reveals the presence of single-domain structures in remanence with strong contrast at the ends of the nanowires, as well as at the transition regions where the diameter is modulated. Micromagnetic simulations suggest that curling of the magnetization takes place at these transition sites, extending over 10–20 nm and giving rise to stray fields measurable with our MFM. An additional weaker contrast is imaged, which is interpreted to arise from inhomogeneities in the nanowire diameter.The authors acknowledge support from the Spanish MINECO under projects CSD2010-00024 and MAT2013-48054-C2-1-R and from the EU commission under project 'REFREEPERMAG' FP7NMP.2011.2.2. info:eu-repo/grantAgreement/EC/FP7/28067

Structural and optical characterization of nanostructured ZnO grown on alumina templates

The growth of nanostructured ZnO thin films on nanoporous anodic alumina substrates (NAAF) by dc reactive magnetron sputtering using a pure Zn metal target is reported. ZnO nanostructures reproduce the pore arrays of the NAAF substrates used as templates mimicking their hexagonal long range order. Stoichiometric nanostructured ZnO samples were grown with wurtzite type structure, highly textured and oriented in the (002) direction. The study of the NAAF pore size effect in the final morphology and optical properties of the nanostructured ZnO is presented for different ZnO thicknesses. The pore size of the nanostructured ZnO films was controlled in the range of 15–65 nm by choosing appropriate NAAF and the sputtering deposition conditions. The broademission band observed in PL spectra of the samples should be associated with color centers transitions (F and H centers) appearing in the alumina templates.Ministerio de Ciencia e Innovación CSD2008-00023Ministerio de Ciencia e Innovación MAT2010-20798-C05-0

Structural and optical characterization of nanostructured ZnO grown on alumina templates

The growth of nanostructured ZnO thin films on nanoporous anodic alumina substrates (NAAF) by dc reactive magnetron sputtering using a pure Zn metal target is reported. ZnO nanostructures reproduce the pore arrays of the NAAF substrates used as templates mimicking their hexagonal long range order. Stoichiometric nanostructured ZnO samples were grown with wurtzite type structure, highly textured and oriented in the (002) direction. The study of the NAAF pore size effect in the final morphology and optical properties of the nanostructured ZnO is presented for different ZnO thicknesses. The pore size of the nanostructured ZnO films was controlled in the range of 15-65 nm by choosing appropriate NAAF and the sputtering deposition conditions. The broad emission band observed in PL spectra of the samples should be associated with color centers transitions (F and H centers) appearing in the alumina templates